Soil formation in technogenic landscapes: trends, results, and representation in the current classifications (Review).pdf Introduction The development of the post-industrial economy does not reduce industrial output or the rate of mineral extraction. On the contrary, the manufacturing productivity increase is accompanied by the transformation of large natural landscapes into technogenic barrens (technogenic landscapes). The formation and structure of technogenic landscapes are governed by human engineering activities to extract and process minerals [1]. Engineering soil transformation has the most significant impact on soils compared to agricultural and urban cases [2] because it leads to a drastic transformation not only of soils themselves but also of all soil formation factors. Soil formation in technogenic landscapes is accompanied by biocenotic succession [3], as well as changes in microclimate, initial substrate properties, and terrain features [4]. As opposed to human-transformed (disturbed) soils, where the natural processes are just corrected, soil-forming processes in technogenic landscapes utilize the “new” substrate [5]. Although some countries faced disturbed area problems as early as the 19th century, technogenic landscapes have become an object of soil research relatively recently. It was facilitated, firstly, by a significant increase in environmental footprint in the second half of the 20th century, and secondly by gaining experience in soil reclamation [6]. Until recently, the research on industrially disturbed territories has covered, mainly, the countries of Europe, the former USSR, and North America. By the beginning of the 1970s, technogenic landscapes were studied in the USA [7, 8], the DDR [9], Great Britain [10], Germany [11], Czechoslovakia [12], and Poland [13]. In Russia, as reported by the Public Committee for Safe Industrial and Mining Practices, by 1965, the reclaimed area exceeded 60.000 hectares [14]. In recent decades, a sharp increase in mineral deposit extraction has occurred in developing countries, so the geography of research has expanded significantly to cover China [15-17], India [18-20], South America [21-23], and Africa [24, 25]. The ever-increasing interest in technogenic landscapes is also related to their significant impact on adjacent areas. Thus, the risk of extreme flooding is higher in areas of intense mining [26-28]. Technogenic landscapes are also subjected to erosion and solifluction processes [21, 29]. Drain water ingress into migration flows affects ground and surface waters [30-32]. Artifacts containing carbonaceous material are prone to spontaneous combustion [33], which reduces the air quality [34]. Technogenic landscapes have not only negative but also some positive effects. In some cases, the fertility of mining waste is higher than that of natural soils [35]. There are cases when soils suitable for plant growth are produced from mining waste. Such waste is prepared by grinding stony fractions, adding active organic matter, and, sometimes, pH neutralization [36]. In the soils of technogenic landscapes, a particular field of study is their carbon sequestration capacity [37-39]. Regardless of the type of activity that produced technogenic landscapes and soils, there are always geochemically (and sometimes geomorphologically) Denis A. Sokolov, Vladimir A. Androkhanov, Evgeny V Abakumov 8 unstable formations. The forces driving the balancing of their surface properties with environmental factors are not only the soil formation drivers but may be caused by pedogenesis. For this reason, the studies of the soils of technogenic landscapes are of great interest. This review analyzes the existing global approaches to soil formation in technogenic landscapes, their reclamation, and their placement in the soil classification system. We consider the soils created through self-remediation or by reclamation of mining waste dumps, mineral processing waste, construction waste, and marine sediments deposited onshore during dredging operations. We paid particular attention to coal mine dump soils, as coal mining is the leading industry that expands technogenic landscapes. In addition, coal is mined on all continents except for Antarctica and in every climatic zone. Characteristic features of soil formation in technogenic landscapes Physical properties of parent materials. Compaction and decompaction. As technogenic landscapes are formed, significant volumes of various substrates are extracted or moved by heavy machinery. As a result, soil formation usually occurs on over-compacted substrates. Even when the process does not include surface leveling or the use of heavy equipment (for example, in water development projects), the soil density of technogenic landscapes is still higher than the density of natural soils in the adjacent areas [40]. While the density of the technogenic landscape soils composed of sandy, loamy and clayey substrates (loose rocks) is in the range of 1.1-1.8 g/cm3, it can reach 2.5 g/cm3 for stony surfaces. In both cases, as soils are formed, the density does not remain constant and changes through two alternating and opposite compaction and decompaction processes [41]. Technogenic soils compaction often continues even after a human activity is completed. For instance, stony soils continue to be compacted regardless of the climatic conditions through packing (shrinkage) of the soil-forming substrate (Table 1). Extra soil compaction occurs when the soils are used for agriculture [42], and, subsequently, as polyculture is replaced by monoculture [43]. The high density of loose soils in technogenic landscapes leads to low water permeability. Therefore, the soil formation on the surface of drill cuttings in a humid climate is hydromorphic [44], which is also detected in moderately humid areas covered by a fertile soil layer [45]. Reducing processes identified by increased methane emission [46] or formation of ferromanganese nodules [47] are detected in the soils formed on stony substrates. Decompaction occurs as a result of root system development initiating the soil structure formation [15]. Because loamy soils contain more material suitable for structure formation than stony soils, their deconsolidation is faster. Spatial and vertical heterogeneity. Heterogeneity is typical of the soils of technogenic landscapes. Spatial heterogeneity (Fig. 1) is found at sites where the surface is composed of various substrates [17, 48]. A pronounced profile Soil formation in technogenic landscapes: trends, results 9 heterogeneity is formed during reclamation, as rocks are laid layer-by-layer. It is also produced as young soil mature. In a humid climate, the textural differentiation of the profile of the technogenic landscape soils is caused by eluvial and illuvial processes [49]. In technogenic formations composed of stony rocks, the soil profile differentiation is due to physical, biophysical, chemical, and biochemical disintegration [50]. It is noted that the intensity of disintegration of coarse rock fragments is higher in arid areas, while for gravel and sand, it is higher in areas with optimal moisture content [51]. Fig. 1. Scheme of the formation of technogenic landscape spatial heterogeneity in surface mining Organic matter accumulation. Soil profile differentiation by organic matter content is a distinctive feature of most technogenic landscapes. Organic matter can be both inherited from soil-forming rocks (lithogenic), e.g., in the soils of coal mine dump, or generated by soil and biological processes. As many authors note (Table 1), the soils of technogenic landscapes, regardless of the rock composition and climatic conditions, feature intense organic matter accumulation rates exceeding those in natural soils. In the areas where organic matter accumulation occurs in zonal soils, organic carbon in technogenic landscapes is fixed by humus accumulation. High organic matter accumulation rates are also found in the soils with soilforming rocks enriched with lithogenic organic matter [61]. The accumulation of humus increases from stony to sandy [58] and further to loamy rocks [82]. In areas where the formation of thick humus horizons is not a feature of the zonal soil formation, the intensity and peculiarities of organic matter stabilization processes in the soils of technogenic landscapes are determined by the lithological properties of the substrates [83]. In the soils enriched with fine fractions (< 0.01 mm), high organic matter accumulation rates can also be found in subtropical and tropical climates [19, 64]. In such areas, they are also found on stony substrates capable of producing fine particles upon weathering [20, 23]. It should be noted that humus accumulation is not the only process of organic carbon accumulation in the soils. о Denis A. Sokolov, Vladimir A. Androkhanov, Evgeny V Abakumov Table 1 Q. g Q. bJ3 О fi Jm ЬХ a *-C 3 -o *c 3 о О. "3 3 з Sо iD СП ’B .2 m S O’- 72 40 S’! £ > 2 сЗ Й N D a ^ Пн ' £2 ^ N D >L) c3 ]--■ W) c3 40 i О Й I C-->л О О О 40 О 1-1 > > о и Table 1 (end) '5 2^ is ^ . 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